The present invention relates to control units which can regulate the flow of hydraulic fluid to and from one or more consumers, and more particularly to improvements in control units wherein the fluid flows to and from one or more consumers by way of one or more fluid flow regulating valves.
It is known to employ in control units for consumers of hydraulic fluid an adjusting apparatus wherein a piston has two end faces of identical cross-sectional area and is mounted between the chambers of a cylinder so that it can move axially and thereby changes the position of the valve member in a fluid flow regulating valve. It is also known to install flow restrictors in conduits which supply fluid to the chambers at the opposite ends of the piston and to control the outflow of fluid from such chambers by resorting to discrete auxiliary valves. The auxiliary valves are operated by solenoids. When the piston has moved the valve member to a selected position (e.g., to an intermediate position between a central or neutral position and one of two end positions), a continuous stream of pressurized fluid flows through one of the chambers, through the respective valve, and back to the tank. This causes substantial losses in pressurized fluid, especially if the valve member is to be held in an intermediate position for extended periods of time. Moreover, control units of the just outlined character require costly linear magnets which also consume energy as long as the valve member of the regulating valve remains in an intermediate position. Still further, the just described control unit employes one or more pressure modulating devices which reduce the pressure of fluid supplied to the adjusting apparatus and exhibit a pronounced tendency to vibrate or oscillate with attendant problems in connection with retention of the valve member in a predetermined position. Finally, the dynamic behavior of the just described conventional control units is far from satisfactory.